Fungal Skin Infections Practice Questions

Q: Skin scraping and KOH mounting is done for what condition?

Fungal infections. **Explanation:** **1. Why Fungal Infections is Correct:** Potassium Hydroxide (KOH) mounting is the **gold standard bedside diagnostic test** for superficial fungal infections (Dermatophytosis, Candidiasis, and Tinea versicolor). The medical principle relies on the fact that KOH is a strong alkali that digests keratin, epithelial cells, and debris in skin scrapings, hair, or nails. Since fungal cell walls contain **chitin**, they remain resistant to KOH. This allows the clinician to clearly visualize fungal elements like hyphae, spores, or budding yeast under a microscope. **2. Why Other Options are Incorrect:** * **Leprosy (A):** Diagnosis is primarily clinical, supported by **Slit Skin Smear (SSS)** using Modified Ziehl-Neelsen staining to identify *Mycobacterium leprae* (acid-fast bacilli). * **Varicella (B) & HSV (D):** These are viral infections. The classic bedside test for these is the **Tzanck Smear**, where a scraping from the base of a vesicle is stained (Giemsa/Wright) to look for **multinucleated giant cells** (Acantholytic cells). **3. High-Yield Clinical Pearls for NEET-PG:** * **Concentration:** 10% KOH is used for skin/hair; 20% KOH is used for thicker nail clippings. * **Classic Morphologies:** * **Dermatophytes:** Translucent, branching, septate hyphae. * **Tinea Versicolor:** "Spaghetti and meatballs" appearance (short hyphae and spores). * **Candidiasis:** Pseudohyphae and budding yeast cells. * **Modification:** **DMSO (Dimethyl sulfoxide)** can be added to KOH to speed up the clearing of keratin without requiring heat.

Q: A patient presents with lesions on the axilla, groin, and trunk. The lesions are characterized by central clearing and a surrounding papulovesicular margin that progressively increases at the borders. Which of the following investigations would be preferred?

10% KOH mount. **Explanation:** The clinical presentation described—lesions with **central clearing** and an **active papulovesicular margin** spreading centrifugally—is the classic hallmark of **Tinea Corporis** (Dermatophytosis). **Why 10% KOH mount is the correct answer:** The 10% Potassium Hydroxide (KOH) mount is the **gold standard bedside investigation** for diagnosing fungal skin infections. KOH acts as a keratolytic agent, dissolving keratinocytes and debris, which allows for the clear visualization of fungal elements under a light microscope. In dermatophytosis, one typically observes **branching, septate hyaline hyphae**. **Analysis of Incorrect Options:** * **A. Wood’s lamp examination:** While useful for Tinea Capitis (e.g., *Microsporum* species) or Erythrasma (coral-red fluorescence), most species causing Tinea Corporis (like *T. rubrum*) do not fluoresce. * **C. Skin biopsy:** This is an invasive procedure generally reserved for atypical presentations or deep fungal infections. It is not the first-line investigation for superficial dermatophytosis. * **D. Patch testing:** This is the investigation of choice for **Allergic Contact Dermatitis**, not fungal infections. **High-Yield Clinical Pearls for NEET-PG:** * **Tinea Incognito:** This occurs when a fungal infection is treated with topical steroids, leading to a loss of the classic annular morphology and making diagnosis difficult. * **Culture Medium:** If KOH is inconclusive but suspicion is high, the gold standard culture medium is **Sabouraud’s Dextrose Agar (SDA)**. * **Erythrasma vs. Tinea:** Erythrasma (caused by *Corynebacterium minutissimum*) lacks the active border and central clearing seen in Tinea and shows coral-red fluorescence under Wood's lamp.

Q: Dhobi's itch is:

Tinea cruris. **Explanation:** **Tinea cruris**, commonly known as **Dhobi’s itch**, is a dermatophyte infection of the groin, perineum, and perianal regions. The term "Dhobi’s itch" originates from the historical association with laundry workers (dhobis) who often wore damp clothes for long periods, creating the warm, humid environment that favors fungal growth. It typically presents as an erythematous, pruritic rash with a well-demarcated, scaly, elevated border and central clearing. **Analysis of Options:** * **Tinea cruris (Correct):** Specifically refers to the fungal infection of the groin. It is most commonly caused by *Trichophyton rubrum* or *Epidermophyton floccosum*. * **Tinea corporis:** Refers to infection of the glabrous skin (trunk and limbs), often called "ringworm." * **Tinea barbae:** A fungal infection of the beard and mustache area, seen primarily in adult males. * **Tinea capitis:** Fungal infection of the scalp and hair shafts, most common in children. **High-Yield Clinical Pearls for NEET-PG:** * **Most common causative agent:** *Trichophyton rubrum* is the most frequent isolate globally for most Tinea infections. * **Sparing of Scrotum:** A key clinical differentiator is that Tinea cruris typically **spares the scrotum and penis**, whereas Candidiasis (Intertrigo) frequently involves the scrotum and presents with "satellite lesions." * **Autoinoculation:** Patients often have concurrent **Tinea pedis** (Athlete's foot); the fungus is transferred to the groin while putting on underwear (feet first). * **Diagnosis:** Confirmed by **KOH mount** showing septate branching hyphae. * **Treatment:** Topical antifungals (e.g., Terbinafine, Clotrimazole) are first-line. Avoid topical steroids as they lead to **Tinea incognito**.

Q: Brown, spherical, septate bodies found in pus are diagnostic of which condition?

Chromomycosis. **Explanation:** The presence of **brown, spherical, thick-walled, septate bodies** (also known as **Sclerotic bodies**, **Medlar bodies**, or **Copper-penny bodies**) in pus or tissue sections is the pathognomonic hallmark of **Chromomycosis** (Chromoblastomycosis). These structures represent the vegetative fungal form and are naturally pigmented due to melanin in their cell walls (dematiaceous fungi). **Why the other options are incorrect:** * **Geotrichosis:** Caused by *Geotrichum candidum*, it typically shows rectangular arthroconidia and true hyphae, not pigmented spherical bodies. * **Mucormycosis:** Characterized by broad, **non-septate (coenocytic)**, ribbon-like hyphae with right-angle (90°) branching. * **Sporotrichosis:** Caused by *Sporothrix schenckii*, it typically presents as **cigar-shaped yeast** cells in tissue. The characteristic clinical finding is "sporotrichoid spread" (nodules along lymphatic drainage). **High-Yield Clinical Pearls for NEET-PG:** * **Causative Agents:** Most commonly *Fonsecaea pedrosoi* and *Phialophora verrucosa*. * **Clinical Presentation:** Usually occurs in barefoot agricultural workers following traumatic inoculation. It presents as slow-growing, **verrucous (warty) plaques** or cauliflower-like lesions, most commonly on the lower limbs. * **Diagnosis:** KOH mount of "black dots" on the lesion surface or biopsy reveals the characteristic **Sclerotic bodies**. * **Treatment:** Itraconazole is the drug of choice; surgical excision or cryotherapy may be used for small lesions.

Q: Scutula is classically seen in which of the following conditions?

Favus. **Explanation:** **Favus** (Option A) is a chronic inflammatory form of Tinea Capitis, most commonly caused by the anthropophilic fungus *Trichophyton schoenleinii*. The hallmark clinical feature of Favus is the **Scutulum**. A scutulum is a yellowish, cup-shaped crust composed of dense masses of fungal mycelia, epithelial debris, and inflammatory cells. These crusts often have a characteristic "mousy odor" and, if left untreated, lead to extensive scarring (cicatricial) alopecia. **Analysis of Incorrect Options:** * **Small spore ectothrix (Option B):** Characterized by fungal spores forming a sheath around the hair shaft. It typically presents as "Gray Patch" tinea capitis with brittle, broken hairs, but does not form scutula. * **Endothrix (Option C):** Spores are found inside the hair shaft (e.g., *T. violaceum*). This leads to the "Black Dot" appearance due to hair breaking at the level of the scalp. * **Kerion (Option D):** An exaggerated inflammatory host response to zoophilic fungi (e.g., *T. verrucosum*). It presents as a painful, boggy, inflammatory mass with pustules and sinus tracts, rather than the dry, cup-shaped crusts of Favus. **High-Yield Clinical Pearls for NEET-PG:** * **Favus Triad:** Scutula, mousy odor, and cicatricial alopecia. * **Wood’s Lamp:** Favus (*T. schoenleinii*) shows a characteristic **dull green** fluorescence. * **Microscopy:** On KOH mount, Favus shows **"Godet" or "Favic chandeliers"** (antler-like branching hyphae) and air bubbles within the hair shaft. * **Treatment:** Oral Griseofulvin remains the traditional gold standard, though Terbinafine is frequently used.

Q: Tinea unguium affects which part of the nail?

Nail plate. **Explanation:** **Tinea unguium** is a dermatophyte infection specifically involving the **nail plate**. The term is often used interchangeably with *onychomycosis*, though the latter technically includes infections caused by non-dermatophyte molds and yeasts (like *Candida*). Dermatophytes are keratinophilic fungi; they thrive on the keratin found in the nail plate, leading to characteristic thickening, discoloration (yellow-white), subungual hyperkeratosis, and onycholysis (separation of the nail plate from the bed). **Analysis of Options:** * **Nail fold (Option A):** Inflammation of the nail folds is termed **Paronychia**. While *Candida* can cause chronic paronychia, dermatophytes (Tinea) primarily target the hard keratin of the plate, not the soft tissue of the folds. * **Joints (Option C):** Fungal infections are superficial or subcutaneous. Joint involvement (Arthritis) is not a feature of Tinea infections. * **Interdigital space (Option D):** Infection of the toe webs is called **Tinea pedis** (Athlete’s foot). While Tinea pedis often coexists with Tinea unguium, they are distinct clinical entities. **High-Yield Clinical Pearls for NEET-PG:** * **Most common organism:** *Trichophyton rubrum* is the leading cause of Tinea unguium worldwide. * **Clinical Patterns:** The most common pattern is **Distal Lateral Subungual Onychomycosis (DLSO)**. * **White Superficial Onychomycosis (WSO):** Characterized by "powdery" white patches on the surface; usually caused by *T. mentagrophytes*. * **Diagnosis:** Potassium hydroxide (KOH) microscopy of nail clippings is the initial screening test; Culture is the gold standard. * **Treatment:** Oral **Terbinafine** is the drug of choice (DOC) for dermatophyte nail infections. Topical lacquers (Ciclopirox/Amorolfine) are used only in mild cases or when systemic drugs are contraindicated.

Q: Which dermatophyte species does not involve the nail?

Microsporum. ### Explanation The correct answer is **Microsporum**. The classification of dermatophytes into three genera—*Trichophyton*, *Microsporum*, and *Epidermophyton*—is based on the specific keratinized tissues they can invade (skin, hair, and nails). **1. Why Microsporum is correct:** *Microsporum* species primarily infect the **hair and skin**. They lack the biochemical capability to effectively invade the nail plate. Therefore, it is the only genus among the three that does not cause Onychomycosis (nail infection). **2. Why the other options are incorrect:** * **Trichophyton:** This is the most versatile genus. It can involve all three keratinized structures: **Skin, Hair, and Nails**. *T. rubrum* is the most common cause of Onychomycosis worldwide. * **Epidermophyton:** This genus involves the **Skin and Nails** but notably **does not involve the hair**. *Epidermophyton floccosum* is a common cause of Tinea cruris and Onychomycosis. **3. High-Yield Clinical Pearls for NEET-PG:** To quickly memorize the tissue involvement, use this simple table: | Genus | Skin | Hair | Nails | | :--- | :---: | :---: | :---: | | **Trichophyton** | Yes | Yes | Yes | | **Microsporum** | Yes | Yes | **No** | | **Epidermophyton** | Yes | **No** | Yes | * **Wood’s Lamp Examination:** *Microsporum* species (like *M. audouinii* and *M. canis*) typically show a brilliant greenish fluorescence, whereas most *Trichophyton* species (except *T. schoenleinii*) do not fluoresce. * **Macroconidia Shape:** *Microsporum* has spindle-shaped macroconidia, *Trichophyton* has pencil-shaped, and *Epidermophyton* has club-shaped macroconidia.

Q: A 24-year-old man presents with multiple small hypopigmented macules around hair follicles on the upper chest and back. Scratching of the lesions with a glass slide reveals fine scaling. What is the investigation of choice for diagnosing this condition?

KOH preparation of scales. ### Explanation The clinical presentation of small hypopigmented macules around hair follicles with fine scaling (evoked by scratching, known as **Besnier’s sign** or the "coup d'ongle" sign) is classic for **Pityriasis versicolor** (Tinea versicolor), caused by the yeast *Malassezia furfur*. **1. Why Option A is Correct:** The investigation of choice for any superficial fungal infection is a **KOH (Potassium Hydroxide) preparation**. When scales from Pityriasis versicolor are treated with 10% KOH, microscopy reveals a characteristic **"Spaghetti and Meatballs" appearance** (or "Banana and Curd" appearance). This represents a mixture of short, thick fungal hyphae and clusters of round yeast cells. **2. Why Other Options are Incorrect:** * **Option B (Tzank test):** Used for diagnosing viral infections (e.g., Herpes Simplex, Varicella) by identifying multinucleated giant cells. * **Option C (Slit Skin Smear):** Primarily used for diagnosing Leprosy (to look for Acid Fast Bacilli) and Leishmaniasis. * **Option D (Skin biopsy):** While it would show fungal elements in the stratum corneum, it is an invasive procedure and unnecessary for a superficial infection that can be diagnosed bedside. **3. High-Yield Clinical Pearls for NEET-PG:** * **Wood’s Lamp Examination:** Lesions show a characteristic **Golden Yellow fluorescence**. * **Culture:** *Malassezia* is lipophilic; it requires the addition of **olive oil** to the culture medium (e.g., Dixon’s agar) for growth. * **Treatment:** Topical antifungals (Ketoconazole shampoo, Selenium sulfide) are first-line. Oral Fluconazole or Itraconazole is used for extensive cases. * **Besnier’s Sign:** The accentuation of fine scales upon scratching the lesion is a pathognomonic clinical sign.

Q: A 19-year-old man develops a rash in the groin area. On examination, it is a large, well-demarcated area of tan-brown discoloration around his left inguinal area. There is some scaling of the lesion when brushed with a tongue depressor. What is the most appropriate initial diagnostic test?

Potassium hydroxide (KOH) preparation of scrapings. **Explanation:** The clinical presentation of a well-demarcated, tan-brown, scaly rash in the inguinal area is highly suggestive of a superficial fungal infection, most likely **Tinea cruris** (jock itch). In any patient presenting with a scaly, erythematous, or pigmented skin lesion suspicious of a fungal etiology, the **Potassium Hydroxide (KOH) preparation** is the gold standard initial diagnostic test. * **Why KOH is correct:** KOH dissolves keratin in skin scrapings, allowing for the clear visualization of fungal elements (septate hyphae and spores) under a microscope. It is rapid, cost-effective, and provides immediate bedside confirmation. * **Why other options are incorrect:** * **Punch biopsy:** This is an invasive procedure reserved for atypical presentations, suspected malignancies, or inflammatory dermatoses that do not respond to treatment. It is not a first-line test for superficial infections. * **Tzanck smear:** This is used for the diagnosis of **herpetic infections** (HSV/VZV) to look for multinucleated giant cells, not fungal infections. * **Blood culture:** This is indicated for systemic/disseminated fungal infections (e.g., Candidemia) in immunocompromised patients, not for localized cutaneous rashes. **NEET-PG High-Yield Pearls:** * **Differential Diagnosis:** If the lesion shows a "coral red" fluorescence under **Wood’s lamp**, the diagnosis is **Erythrasma** (caused by *Corynebacterium minutissimum*), which can mimic Tinea cruris but lacks hyphae on KOH. * **Tinea Cruris:** Usually spares the scrotum (unlike Candidiasis, which involves the scrotum and presents with satellite lesions). * **KOH Findings:** Look for "branching hyphae" in Dermatophytosis and "spaghetti and meatballs" appearance in Tinea versicolor.

Q: Tinea unguium involves which of the following structures?

Nails. **Explanation:** **Tinea unguium** is a dermatophyte infection specifically involving the **nails** (Option B). The term is derived from "Tinea" (fungal skin infection) and "Unguium" (referring to the nail plate, from the Latin *unguis*). While it is often used interchangeably with "onychomycosis," the latter is a broader term that includes infections caused by dermatophytes, yeasts (Candida), and non-dermatophyte molds. **Why other options are incorrect:** * **A. Hands:** Fungal infection of the dorsal aspect of the hand is called **Tinea manuum**. * **C. Palm:** This is also classified under **Tinea manuum**, often presenting as diffuse hyperkeratosis. * **D. Foot:** Fungal infection of the foot (interdigital spaces, soles, or borders) is known as **Tinea pedis** (Athlete’s foot). **High-Yield Clinical Pearls for NEET-PG:** 1. **Etiology:** The most common causative agent for Tinea unguium worldwide is ***Trichophyton rubrum***. 2. **Clinical Variants:** The most common pattern is **Distal Lateral Subungual Onychomycosis (DLSO)**. White Superficial Onychomycosis (WSO) is often associated with *T. mentagrophytes*. 3. **Proximal Subungual Onychomycosis (PSO):** This is a rare variant in the general population but is considered a **strong clinical marker for HIV/AIDS**. 4. **Treatment of Choice:** Oral **Terbinafine** is the gold standard. Griseofulvin is generally ineffective for nail infections due to poor penetration and long treatment durations. 5. **Diagnosis:** Confirmed by KOH microscopy (showing hyphae) or fungal culture on Sabouraud’s Dextrose Agar (SDA).

Question 1

Skin scraping and KOH mounting is done for what condition?

Accepted Answer

Fungal infections

Answer

Leprosy

Answer

Varicella

Answer

Herpes Simplex Virus (HSV)

Question 2

A patient presents with lesions on the axilla, groin, and trunk. The lesions are characterized by central clearing and a surrounding papulovesicular margin that progressively increases at the borders. Which of the following investigations would be preferred?

Accepted Answer

10% KOH mount

Answer

Wood's lamp examination

Answer

Skin biopsy

Answer

Patch testing

Question 3

Dhobi's itch is:

Accepted Answer

Tinea cruris

Answer

Tinea corporis

Answer

Tinea barbae

Answer

Tinea capitis

Question 4

Brown, spherical, septate bodies found in pus are diagnostic of which condition?

Accepted Answer

Chromomycosis

Answer

Geotrichosis

Answer

Mucormycosis

Answer

Sporotrichosis

Question 5

Scutula is classically seen in which of the following conditions?

Accepted Answer

Favus

Answer

Small spore ectothrix

Answer

Endothrix

Answer

Kerion

Question 6

Tinea unguium affects which part of the nail?

Accepted Answer

Nail plate

Answer

Nail fold

Answer

Joints

Answer

Interdigital space

Question 7

Which dermatophyte species does not involve the nail?

Accepted Answer

Microsporum

Answer

Trichophyton

Answer

Epidermophyton

Answer

None of the above

Question 8

A 24-year-old man presents with multiple small hypopigmented macules around hair follicles on the upper chest and back. Scratching of the lesions with a glass slide reveals fine scaling. What is the investigation of choice for diagnosing this condition?

Accepted Answer

KOH preparation of scales

Answer

Tzank test

Answer

Slit Skin Smear Examination

Answer

Skin biopsy of lesion

Question 9

A 19-year-old man develops a rash in the groin area. On examination, it is a large, well-demarcated area of tan-brown discoloration around his left inguinal area. There is some scaling of the lesion when brushed with a tongue depressor. What is the most appropriate initial diagnostic test?

Accepted Answer

Potassium hydroxide (KOH) preparation of scrapings

Answer

Punch biopsy of skin

Answer

Tzanck smear

Answer

Blood culture for fungi

Question 10

Tinea unguium involves which of the following structures?

Accepted Answer

Nails

Answer

Hands

Answer

Palm

Answer

Foot

Fungal Skin Infections — MCQs

Fungal Skin Infections — MCQs

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